Applying comments + added check for negative value of source

Author: Pashchenkov Maxim

demos/gesture_recognition_demo/cpp_gapi/README.md

@@ -22,9 +22,9 @@ The demo workflow is the following:
 
 > **NOTE**: By default, Open Model Zoo demos expect input with BGR channels order. If you trained your model to work with RGB order, you need to manually rearrange the default channels order in the demo application or reconvert your model using the Model Optimizer tool with the `--reverse_input_channels` argument specified. For more information about the argument, refer to **When to Reverse Input Channels** section of [Converting a Model Using General Conversion Parameters](https://docs.openvino.ai/latest/openvino_docs_MO_DG_prepare_model_convert_model_Converting_Model.html#general-conversion-parameters).
 
-## Creating a Gallery for gestures window
+## Creating a Gallery for Gestures Window
 
-The gallery of sample videos can be created to show the sample gestures on an additional window:
+The gallery of sample videos and list of paths to gesture videos must be created to show the sample gestures on an additional window:
 
 1. Put videos containing gestures to a separate empty folder. Each video must have only one gesture.
 2. Run the `python3 <omz_dir>/demos/gesture_recognition_demo/cpp_gapi/create_list.py --classes_map <path_to_a_file_with_gesture_classes> --gesture_storage <path_to_directory_with_gesture_videos>` command, which will create a `gesture_gallery.json` file with list of gestures and paths to appropriate videos.

demos/gesture_recognition_demo/cpp_gapi/create_list.py

@@ -20,7 +20,7 @@
 import json
 import argparse
 
-parser = argparse.ArgumentParser(description='')
+parser = argparse.ArgumentParser()
 
 parser.add_argument('--gesture_storage',
                     help='Path to the gesture directory')

demos/gesture_recognition_demo/cpp_gapi/include/stream_source.hpp

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <utils/images_capture.h>
+#include <utils/slog.hpp>
 #include <opencv2/gapi.hpp>
 #include <chrono>
 #include <thread>
@@ -93,7 +94,12 @@ class CustomCapSource : public cv::gapi::wip::IStreamSource
                              const cv::Size& frame_size,
                              const int batch_size,
                              const float batch_fps)
-        : cap(cap), producer(batch_size, batch_fps) {
+        : cap(cap), producer(batch_size, batch_fps), source_fps(cap->fps()) {
+        if (source_fps <= 0.) {
+            source_fps = 30.;
+            wait_gap = true;
+            slog::warn << "Got a non-positive value as FPS of the input. Interpret it as 30 FPS" << slog::endl;
+        }
         /** Create and get first image for batch **/
         GAPI_Assert(first_batch.empty());
         if (batch_size == 0 || batch_size == 1) {
@@ -119,6 +125,8 @@ class CustomCapSource : public cv::gapi::wip::IStreamSource
 protected:
     std::shared_ptr<ImagesCapture> cap; // wrapper for cv::VideoCapture
     BatchProducer producer; // class batch-construcor
+    double source_fps = 0.; // input source framerate
+    bool wait_gap = false; // waiting for fast frame reading (stop main thread when got a non-positive FPS value)
     bool first_pulled = false; // is first already pulled
     std::vector<cv::Mat> first_batch; // batch from constructor
     cv::Mat fast_frame; // frame from cv::VideoCapture
@@ -147,6 +155,14 @@ class CustomCapSource : public cv::gapi::wip::IStreamSource
 
         /** Put fast frame to the batch **/
         producer.fillFastFrame(fast_frame);
+        if (wait_gap) {
+            const auto cur_step = std::chrono::steady_clock::now() - read_time;
+            const auto gap = std::chrono::duration_cast<std::chrono::milliseconds>(cur_step).count();
+            const int time_step = int(1000.f / float(source_fps));
+            if (gap < time_step) {
+                std::this_thread::sleep_for(std::chrono::milliseconds(time_step - gap));
+            }
+        }
 
         /** Put pulled batch to GRunArg data **/
         cv::detail::VectorRef ref(std::move(producer.getBatch()));